Step 1: The Situation

Due to circumstances beyond my control, my cubicle at work is close to both the break room and a small loading area on the second floor. Because of this I usually have a wall of boxes filled with copier paper situated somewhere behind me. Aside from this being a nuisance when it comes to concentrating on my job it also affords me the opportunity to scavenge as many copier boxes that a man can get his hands on.

Step 2: The Result

Behold! My dashboard cooking days are over. I present to you The Office Worker’s Solar Oven. This project was built completely with materials laying about the office, with the exception of tinfoil, which I picked up at the dollar store.

Step 3: Gathering the pieces

Above you can see all the precut pieces to form the main cooking chamber. I cut the box at an angle of 20 degrees to allow for maximum exposure to the sun. In my latitude the lowest elevation that the sun gets is 26 degrees above the Southern horizon.

Be sure to cut your box accordingly if you plan to make one.

Step 4: A little design consideration

I designed the oven to allow for one inch of insulation on each side of the box. To do this I placed slots in the inside liner. This is the back piece.

Step 5: More design consideration

These are the sidepieces, slotted as well. I also cut these with an angle of 20 degrees.

Step 6: Some Assembly Required

As you can see the slotted pieces fit together nicely.

Likewise the liner fits nicely into the oven box.

Step 7: The Insulated Floor

Once I was sure that everything fit together, I removed all the pieces and put a one-inch spacer in the bottom of the box to keep the bottom of the oven above a layer of insulation.

The insulation I used was just shredded documents I salvaged from the office shredder.

with regard to the reflective aspects of alu foil, that is a much 'heated' discussion. Apparently it is abt 50% and with that it is less than a white surface. Perhaps it would have been better to just line yr oven with white paper. That would have saved a run to the dollar store. :-)

You are correct, and in reality the list I can now form that would improve this project is far too long for me to even consider at this point seeing as how I have moved on to other things, namely http://zerosumhacker.blogspot.com/ :D

Fantastic instructable! I wonder if you would get more heat by painting the interior black to absorb light and heat to the box would work better than using foil. You still see people (thankfully not in my neighborhood) using foil on home windows to reflect light and heat away. You could use an outside hood (outside the main box) covered in foil to direct the light in (like a satalitte dish focusing on a smaller point) and use black paint on the inner box to absorb the heat.

I think it all depends on where you want the heat to go and what you want it to heat. It was my intention to bounce the light around inside the box and have it ultimately hit a black target that would absorb the heat.

In retrospect I see several areas for improvement of the model I presented here. But in reality I wanted to limit myself to what I have available around the office and of course I wanted to have fun.

Fantastic Instructable! Thanks for all the pics, the well explained directions, the quantification, and most importantly, for your time.

I would like to echo what Haw1horne said: Heating plastic is a bad idea unless it is designed for heating. You may not see or taste the outgassed products, but they are there. Other sites also say that if you can't use glass then the baking bags will work. I think a layer on the inside of the cover sealed with a cardboard edge, and another layer on the outside of the cover also sealed. Of course, pull tight to reduce diffraction.

An aside to the previous; careful what paint you use. Some are not safe to be heated. Look for those labeled as non-toxic stove paint.

A glass top would help keep the lid sealed because of its additional weight. If you go with the turkey bag window route, I'm thinking paperclip and rubber band anchoring system around the outside would keep things tight and allow for less heat loss. My guess is this is where your heat loss came from.

An angled lid lined with foil (aluminum, tin, lead, mylar, whatever) would catch more light and protect the works when all finished and folded down.

I'll start my oven tomorrow. Again, fantastic job with this and thank you so much for your time and effort.

if the insulation is to keep the heat in, i would suggest the paper shreds AND, a layer of mylar emergency blanket cut accordingly to fit the walls. because it reflects heat it is a good material to use for this, you can get them for like 7bucks online.

you, sir, are EXTREMELY good at making instructables. you were able to show how to make an oven (although you didnt really provide enough detail, but im sure the pictures are good enough for someone to tell what to do) andyou even did the math for us to show how hot it gets and all the important things the oven does. i salute you =]]

True! haha - although for information's sake (in case there was ever any kind of specific need for *tin* foil as opposed to aluminum), they actually still make tin foil these days - you can find it at florists shops that carry it. It's often preferred over aluminum at such places for some reason or other.

I wonder how much hotter it would've gotten in there, if say, instead of the trash bag plastic, you used one of those cheap, acrylic/plastic, 8.5x11" Fresnel lens thingies - they don't jjust focus light, but heat as well... I think I'll try that at some point between instrumennt projects.

I think you'll find that lenses DO just focus light. The heat is created as a result of that light, so obviously by focusing the light to a smaller area > higher intensity > greater heat. However, the advantages of that increase in light intensity would be restricted to the focal point, I think, as it's the same amount of total light going through the window/lens.

The real trick here, I suspect, is maximising insulation on all sides and the area of the window, while minimising total volume. Afterall, the more air inside, the more air to heat up.

You can only make it so small, though, before you're not collecting enough light to make the efficiency worth it. Wouldn't a more finely-tuned reflection chamber help more? Most solar ovens I've seen use a parabolic surface to not only collect sunlight, but also focus it on the object to be heated. I haven't seen one that's just a reflective box before. (Not that I know much about solar ovens or have researched or anything...) Is there a reason that wasn't done here, I wonder?

I wonder how much light gets lost from diffusion by the trash bag, too. Probably not much, but it would be interesting to compare it with glass. (There's gotta be a broken flatbed scanner around the office somewhere...)

Yes, true - and as a result, it does focus heat as well as light... a bit of an "accidental quality" perhaps, but yeah. Seems you and both I agree on this, it's just that I'm just saying things kinda weird here hehe ^_~

But yeah, what with the way a Fresnel lens focuses light into a concentrated beam (much as lighthouses do), so does the heat concentrate, as well. Like with one of those Fresnel lens panels that can be gotten through Edmund Scientifics that can melt asphalt, for instance. As far as a focal point, with a Fresnel lens, it's a beam (again, like with lighthouse lenses, which are of the Fresnel type), so there's not much as far as spacial restrictions go, I would imagine. But I could be wrong. I'm no scientist lol

True that, on the insulation... but with a focused beam (as opposed to an apex/singular focal point) and spacially-throughout-heat-intensity, there *may* be a need for more heat resistant materials... hmmm... insulative fiberglass, perhaps? Like the kind one can find in one's attick? Maybe...

There's 3 complications with your implementation of the solar box oven (variation of the Kerr/Cole Oven patented in the 1980s)

One is the plastic glazing. If the oven did get hot enough, that sheet would very likely melt, warp, and/or outgas. This could be bad for your lunch! In any event, its probably not a food-safe grade of plastic if you found it around the work place. One work around is to use food-grade turkey bag plastic. Stretch it tight across a frame, and mount the frame in the lid.

Second is the plastic glazing. Yes, I know that sounds redundant. The biggest source of heat leaking is going to be out through that plastic. You can improve this by either using glass or lexan for the glazing, or by creating a double layer of food-grade plastic with a 1/4" gap in between the layers.

Third, most box ovens made for climates outside the Tropics have an additional reflector to help boost the heat up to cooking temperatures. Cookers that don't have the additional reflector are (1) Made for the tropics (2) Use double glazing (3) Use high-R polyisocyanurate insulation in the walls.

the grocery store has inexpensive oven bags- if you put your food container (painted black) inside the bag, then capture air around it and close off with a rubber-band, you get excellent insulation (and easy cleanup in the event of a spill).

also painting the interior black might help, as would raising your food container so that the light reflected off of the foil will hit all sides of the container

Nice build! I'm impressed that you made this with all reclaimed materials (and time) from work. There's nothing like a little creative goofing off on the job to keep your mind fresh. Thanks for doing the math. It was a very professional touch and it makes others think about their project in terms of measurable success Keep up the good work..